1. Field of the Invention
The present invention relates to an improvement of a magnetic recording medium, and more particularly to a magnetic recording medium which is excellent in the lubricity and wear resistance.
2. Description of the Prior Art
A magnetic recording medium comprises a support such as of polyethylene terephthalate, polyethylene-2,6-naphthalate, or the like, having directly or through a subbing layer thereon a magnetic layer containing ferromagnetic powdery material, and further having, if necessary, on the magnetic layer thereof and/or on the back of the support thereof an overcoat layer and/or backcoat layer, respectively. In the recording or reproduction of information, the magnetic recording medium is scanned with being rubbed by a magnetic head. Further the relative speed between the recording medium and the recording head is very high (e.g., from 19 to 38 cm/sec.) and, besides, during the record reproduction, the recording head vigorously rubs the running recording medium, so that the wear resistance and life of the recording medium, when repeatedly used, come into question.
In order to cope with such problems, for example, as is described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 39402/1974, a magnetic recording medium treated over the magnetic layer surface thereof with a lubricant such as graphite, molybdenum dioxide, castor oil, olive oil, or the like, may be used, but these treatments are not considered to provide as much sufficient lubricity as to withstand the use over an extensive period of time.
In order to overcome the shortcoming of such techniques of the prior art, Japanese Patent O.P.I. Publication No.39402/1974 proposes coating over a nonmagnetic support a mixture of a boron compound with a binder, in a proportion of 1.0-1.5 parts by weight of the compound to 100 parts by weight of the binder, along with a ferromagnetic powdery material, the said compound having the formula: ##STR2##
However, the above compound is a low-molecular compound and is one mixed as an additive into a binder, so that if the compound is added in a quantity exceeding a given limit to raise its lubricating effect, the effect becomes saturated, and on the contrary it increases the "blooming phenomenon," thus causing it to become eventually unable to be used because of its undesirable phenomenon.